1. Field of the Invention
The present invention relates to a shutter abnormality detection apparatus for a camera.
2. Description of the Related Art
A camera on which a focal plane shutter is mounted has heretofore been known. In this camera, an electric control type shutter is used which includes two curtains of leading and trailing curtains and which electrically runs the leading and trailing curtains to control the shutter.
In this electric control type shutter, it is known that an abnormal operation of the shutter is electrically detected and warning is given.
A typical shutter abnormality is “non-exposure”, and this abnormality indicates that a photograph is not exposed despite of a release operation performed by a photographer.
There are roughly two causes for generation of the non-exposure. One is that dust, and the like adhere to an attracting surface of a magnet engaging the leading and trailing curtains and the magnet causes an attraction defect. The other is that a driving mechanism of the shutter curtain becomes defective or the shutter curtain per se is deformed and the shutter curtain cannot run.
For a trouble of the non-exposure, the abnormality is not found until a film is developed. This is a large trouble for the camera. Therefore, some techniques of the warning of the abnormality at a photographing time have been proposed.
For example, in U.S. Pat. No. 5,257,056, a leading curtain detection switch and a trailing curtain detection switch are disposed, and a predetermined warning is issued, when the abnormality of the curtain is detected before/after driving the shutter. In U.S. Pat. No. 5,758,213, a reflective optical sensor is disposed in a shutter portion, and this sensor detects a run timing, exposure time or speed of the curtain and issues the warning.
The driving mechanism of the shutter varies also with a maker or a camera type. Therefore, various “defects of the driving mechanism of the shutter curtain” which are causes for the non-exposure are considered.